Nuclear factor κB (NF-κB) is an important transcriptional regulator that is involved in numerous cellular processes, including cell proliferation, immune response, cell survival, and malignant transformation. It relies on the ubiquitin–proteasome system (UPS) for several of the steps in the concerted cascade of its activation. Previously, we showed that the ubiquitin (Ub) ligase KPC1 is involved in ubiquitination and limited proteasomal processing of the NF-κB1 p105 precursor to generate the p50 active subunit of the “canonical” heterodimeric transcription factor p50–p65. Overexpression of KPC1 with the generation of an excessive amount of p50 was shown to suppress tumors, an effect which is due to multiple mechanisms. Among them are suppression of expression of programmed cell death-ligand 1 (PD-L1), overexpression of a broad array of tumor suppressors, and secretion of cytokines which results in recruitment of suppressive immune cells into the tumor. Here, we show that the site of KPC1 to which p105 binds is exceptionally short and is made up of the seven amino acids WILVRLW. Attachment of this short stretch to a small residual part (∼20%) of the ligase that also contains the essential Really Interesting New Gene (RING)-finger domain was sufficient to bind p105, conjugate to it Ub, and suppress tumor growth in an animal model. Fusion of the seven amino acids to a Von Hippel–Lindau protein (pVHL)-binding ligand (which serves as a “universal” ligase for many proteolysis-targeting chimeras; PROTACs) resulted in a compound that stimulated conjugation of Ub to p105 in a cell-free system and its processing to p50 in cells and restricted cell growth.

核因子 κB (NF-κB) 是一种重要的转录调节因子，参与许多细胞过程，包括细胞增殖、免疫反应、细胞存活和恶性转化。它依赖于泛素-蛋白酶体系统 (UPS) 来完成其协同级联激活的几个步骤。以前，我们发现泛素 (Ub) 连接酶 KPC1 参与泛素化和有限的 NF-κB1 p105 前体蛋白酶体加工，以产生“经典”异二聚体转录因子 p50-p65 的 p50 活性亚基。KPC1 的过度表达和过量 p50 的产生被证明可以抑制肿瘤，这是由多种机制引起的。其中包括抑制程序性细胞死亡配体 1 (PD-L1) 的表达，大量肿瘤抑制因子的过度表达和细胞因子的分泌，导致抑制性免疫细胞募集到肿瘤中。在这里，我们展示了与 p105 结合的 KPC1 位点非常短，由 7 个氨基酸 WILVRLW 组成。将这个短片段连接到连接酶的一小部分（~20%）上，该部分也包含必需的真正有趣的新基因（RING）-指结构域，足以结合 p105，与 Ub 结合，并抑制肿瘤生长。动物模型。七个氨基酸与 Von Hippel-Lindau 蛋白 (pVHL) 结合配体的融合（作为许多蛋白水解靶向嵌合体的“通用”连接酶；